With a navigating tanker, various forces act on the hull. For example, the hull itself is subjected to a longitudinal bending moment and torsional forces, the outer bottom plating and the outer side plating to the pressure of water, and the inner bottom plating and side wall of the hold (oil tank) to the load of oil cargo under gravity. To withstand these forces, the hull includes a large number of reinforcing members such as longitudinal members (side longitudinal members, bottom longitudinal members, central girder, etc.) extending longitudinally of the ship and transverse members (side transverse members, bottom transverse members, etc.) provided transversely of the ship. In the case of such a structure, however, longitudinal members and transverse members are provided in an intersecting arrangement, so that difficulties are encountered in building the hull by automatic work procedures (e.g. automatic welding). To assure automatic work procedures, therefore, a double hull structure has been proposed which includes no other transverse members besides transverse bulkheads and which comprises an inner hull plating and an outer hull plating connected together only by the transverse bulkheads and connecting longitudinal members fixed to the transverse bulkheads (For simplicity, a ship of such a structure is hereinafter referred to as "transverseless ship", the term "transverseless" in this case meaning the absence of reinforcing transverse members.). In this case, however, forces acting on the inner and outer hull platings are all transmitted to the transverse bulkheads through the connecting longitudinals, so that the proposed structure has problems in respect of strength when the transverse bulkheads are of conventional structure.